This invention is directed to a process for the coagulation of an aqueous polymer latex. More specifically, this invention concerns a process, as aforesaid, wherein an aqueous polymer latex is contacted with an effective amount of a coagulant which is an aqueous solution of a water soluble non-nucleophilic, non-oxidative salt of an alkaline earth metal. This invention also concerns polymers prepared by the process.
Coagulation of a polymer latex is well known. For example, U.S. Pat. No. 3,751,527 is directed to the blending of two polymers, which may be the same polymer or different polymers, in an extruder. U.S. Pat. No. 3,751,527 teaches that a coagulant solution may be composed of any of a number of salts such as sodium chloride, and polyvalent metal salts such as calcium chloride, aluminum chloride or aluminum sulfate. The disclosure of U.S. Pat. No. 3,751,527 is incorporated herein by reference.
U.S. Pat. No. 2,516,980 discloses incorporating, into a synthetic hydroxylated polymer, a minor amount by weight of a hypophosphorous acid compound to reduce discoloration of a hydroxylated polymer at elevated temperature. Among the compounds which the U.S. Pat. No. 2,516,980 teaches incorporating into a solution of the hydroxylated polymer are sodium hypophosphite, as well as the ammonium and alkali and alkaline metal salts such as potassium, calcium, magnesium, barium and ammonium hypophosphites. This patent fails to teach the use of an alkaline earth metal salt, contemplated herein, for coagulating a polymer latex and instead is directed to treating a polymer solution or a polymer fabric, yarn or film.
U.S. Pat. No. 2,548,974 is directed to a method of making rubbery articles which are deposited directly from an aqueous dispersion of rubber-like material. The U.S. Pat. No. 2,548,974 patent teaches that a method for making rubbery deposition articles includes a method for leaching coagulant from a rubbery coagulum deposit in a short time without introducing a large amount of water into the deposit. The U.S. Pat. No. 2,548,974 exposes a coagulum deposit to water vapor and teaches that an aqueous coagulant-containing liquid accumulates between the article and a suitably shaped form. The coagulants which may be leached in accordance with the teachings of the U.S. Pat. No. 2,548,974 are water soluble polyvalent metal salts of inorganic or organic acids such as calcium nitrate or of water soluble ionizable acids such as acetic acid. The U.S. Pat. No. 2,548,974 fails to teach or suggest any of the novel coagulants used herein.
U.S. Pat. No. 2,576,720 is directed to the granular polymerization of a material such as methyl methacrylate in order to obtain the polymer in granular form. Also disclosed is the granular polymerization of styrene and vinyl acetate. The U.S. Pat. No. 2,576,720 teaches the use of sodium or potassium hypophosphite as an anti-clustering agent in preparing the aforesaid polymers. By the term clustering, the U.S. Pat. No. 2,576,720 sets forth that what is meant is the agglomeration of fine polymer granules to form aggregates of larger and widely varying sizes. The U.S. Pat. No. 2,576,720 fails to teach or suggest the invention described herein.
U.S. Pat. No. 3,896,093 is directed to a process for the recovery of polymers of acrylonitrile and styrene and optionally, butadiene, by coagulation of aqueous latices containing these polymers. The U.S. Pat. No. 3,896,093 teaches that coagulants such as hydrochloric acid, sulfuric acid, formic acid, and water soluble salts of chlorides, nitrates, sulfates and acetates of sodium, potassium, calcium, magnesium, zinc, and aluminum may be used as the coagulants. The U.S. Pat. No. 3,896,093 does not teach the use of non-nucleophilic, non-oxidative coagulants.
U.S. Pat. No. 3,915,909 is directed to a process for isolating rubbers from their aqueous dispersions (latices). The process involves adding an alkyl cellulose or a hydroxyalkyl cellulose to an aqueous rubber dispersion and adding a water soluble alkali metal salt or alkaline earth metal salt, aluminum salt or zinc salt to the dispersion. None of the salts which are added are non-nucleophilic and non-oxidative.
U.S. Pat. No. 3,160,620 is directed to the coagulation of chloroprene polymer latices and isolation of the polymer therefrom. The U.S. Pat. No. 3,160,620 teaches that the aqueous coagulating solution contains a water soluble calcium salt and hydroxyethyl cellulose and a water soluble salt of a water insoluble carboxylic acid. The U.S. Pat. No. 3,160,620 teaches that all of the three components, set forth above, are necessary to obtain the benefits of the U.S. Pat. No. 3,160,620. The U.S. Pat. No. 3,160,620 teaches the use of coagulants such as a water soluble calcium salt which may be the nitrate, chloride, bromide, thiocyanate, and acetate. The U.S. Pat. No. 3,160,620 fails to teach or suggest a non-nucleophilic, non-oxidative coagulant and a polymer obtained thereby.
All of the prior art processes, which utilize coagulants to coagulate a polymer from a polymer latex, suffered from the disadvantage that the very nature of the prior art coagulants served to introduce additional precipitating additives to a material which already contained residues from emulsifier, polymerization initiator, and other components which, although necessary to the process, also served to introduce contaminants into the final polymer and thus into articles prepared from the final polymer. These diluents or contaminants have an adverse effect on polymer properties and on articles made from the resultant polymer. It was not possible, until the present invention, to prepare polymers and articles fabricated therefrom which have a unique combination of water haze properties, yellowness index properties and light transmission properties.
It is an object of this invention therefore to provide a process for the coagulation of a polymer latex.
Another object of this invention is to provide a process for the coagulation of a polymer latex wherein residual coagulant does not substantially affect the properties of the polymer obtained therefrom.
A still further object of this invention is to provide a clear transparent solid polymeric article which has a combination of enhanced properties of water haze value, yellowness index and light transmission.
Other objects and advantages will become apparent from the following more complete description and claims.